cleanup broadcaster dependency

Author: dignifiedquire

Diff for: Cargo.toml

@@ -31,7 +31,7 @@ default = [
   "pin-project-lite",
 ]
 docs = ["attributes", "unstable", "default"]
-unstable = ["std", "broadcaster"]
+unstable = ["std"]
 attributes = ["async-attributes"]
 std = [
   "alloc",
@@ -55,7 +55,6 @@ alloc = [
 [dependencies]
 async-attributes = { version = "1.1.1", optional = true }
 async-task = { version = "3.0.0", optional = true }
-broadcaster = { version = "1.0.0", optional = true }
 crossbeam-utils = { version = "0.7.2", optional = true }
 futures-core = { version = "0.3.4", optional = true, default-features = false }
 futures-io = { version = "0.3.4", optional = true }